The effects of RET on process capability for 45nm technology node

Abstract

One of the main factors driving ICs in complexity is the improvement in photolithography to print small features. The use of immersion imaging and resolution enhancement technology (RET) will extend the ArF lithography to produce small features. With the patterns size decreasing, the absolute CD variation has a bigger relative importance on small features. The process windows are used to see if a certain process is compatible with the dose and focus budget. We discuss the impact of illumination, numeric aperture, phase-shifting mask and polarized light on process windows using ArF immersion lithography to print line pattern exposed features in photo resist on 45nm node. The interaction between the process windows and illumination, numeric aperture, phase-shifting mask and polarized light are calculated using a full photo resist model. The analysis gives fundamental insight into the optimum conditions necessary for printing these patterns both individually and simultaneously. The results show that illumination, numeric aperture, phase-shifting mask and polarized light can contribute to the process capability. The dipole illumination system can enhance the process window about twice than that use conventional illumination. The process capability of semi-dense pattern is insensitive to optical parameters. The 100% attPSMs and altPSMs are strong phase shifting mask, so the process capability can be enhanced. By using the polarized light can enlarge the depth of focus about 4%~11% with specified exposure latitude. According to the rules of process windows, some methods to extend process windows are presented.